27 replies to this topic

[pianodoc]

I recently purchased a Celestron 9.25 on a GEM II mount and I’m very grateful to advice that I received from this group. Now I need to buy some eyepieces. I’ve learned a lot from this forum and other sources including the amazing lecture from Chris Stewart that was recommended here as well. I understand the basics and then some, however I do have 2 questions:
1. I want to get some 2 inch eye pieces but my visual back is for 1.25. Well I lose anything if I use an adapter or do I need to replace the visual back?
2. From my reading, I will probably stick with Plossls, but do you recommend any specific brands over others?
I will be doing both planetary and deep sky observing.

Thank you very much in advance, and Happy Easter to those who celebrate!

[cookjaiii]

You need to replace the visual back to avoid vignetting   

 

Vixen and Televue both make excellent Plossls.  I'm sure there are others, but those two I have personal experience with.  Good Plossls are easier to make than a lot of other eyepieces, so the polish and coatings are where you find the differentiation. 

 

Congrats on the new scope!

[jrmacl]

Also the sv207 Plossl is the same as the vixen but less expensive, although they only have a couple of the sizes. They are always out of the 30mm but most comment they like the eyecup on the vixen model better so...

 

https://www.svbony.c...yepiece/#W9158C

 

they also have, for even less, their sv131 Plossl, I just got the 32mm, it works fine for me

 

I also just bought their sv135 7-21mm zoom and although not quite as good as my TV Plossls, it is certainly fun to use and for the price I would recommend that 

[jrmacl]

and there is really only the 55mm-56mm size that you would need a 2" diagonal for if you are planning on sticking with Plossls, unless maybe you are talking about the MOP's or maybe the 48mm Brandon or the 50mm TPL, for that I would think you would need the full 2" aperture so any adapters that reduce that probably won't work

Edited by jrmacl, 20 April 2025 - 02:12 PM.

[eblanken]

Hello (aka Pianodoc),

 

Welcome to Cloudy Nights ! Congrats on your new (to you) 9.25 inch SCT on GEM.

 

I own Meade 8 inch SCTs. I went the route to get SCT Diagonals for each of them so that I could use 2 inch eyepieces. Others take a different approach and get focal reducers to stay with 1.25 inch eyepieces. I respect them, but I'm in the camp of using 2 inch eyepieces. 

 

One consequence of going with a 2 inch visual back and 2 inch diagonal is that the primary to secondary mirror spacing changes when the extra optical path that a 2 inch diagonal is introduced. So for my 8 inch SCTs, the 203mm x 2,000mm, f/10 becomes 203mm x 2,200mm, f/11 (approx). This is not a bad thing, but it does affect the magnification and eyepiece selection: What I thought was 40x with a 50mm Plossl Eyepiece was actually 44x. After I learned this, I obtained a 55mm Televue Plossl and that got me back to 40x in my scope.

 

The up-side is that 2 inch eyepieces do facilitate the widest True Field of View (TFoV) that the SCT is capable of having and largest Exit Pupil (EP) as well. In my SCTs, as well as the TeleVue Plossl 55mm, I use Pentax XW 68 Deg. eyepieces: 40mm, 30mm at 2 inch . I also have Vixen LVW 42mm as well and even have a Clave' 50mm Plossl too.

 

I agree with (aka cookjaiii): "You need to replace the visual back to avoid vignetting"

 

Very Best Regards,

 

Ed

 

P.S. Happy Easter to you, (aka Pianodoc), as well . . . Private Message (PM) me if you want . . . 

Edited by eblanken, 20 April 2025 - 02:17 PM.

[Inkie]

https://www.cloudyni...eces-announced/

 

I think you have much to gain by spending some dough and swapping out the visual back.  You can hope to get a first class optical set (that scope is particularly known as an excellent SCT, usually very sharp),  and continue to use 1.25" eyepieces when seeing and your interest come together on those special nights, especially for lunar, planetary, and double star splitting and you need more magnification. You'll just have to make allowances with an adapter inserted into the diagonal, and maybe you'll have some obvious vignetting...?  Someone who knows this will pipe up.

[eblanken]

Hi Again,

 

Also the sv207 Plossl is the same as the vixen but less expensive, although they only have a couple of the sizes. They are always out of the 30mm but most comment they like the eyecup on the vixen model better so...

 

https://www.svbony.c...yepiece/#W9158C

 

they also have, for even less, their sv131 Plossl, I just got the 32mm, it works fine for me

 

I also just bought their sv135 7-21mm zoom and although not quite as good as my TV Plossls, it is certainly fun to use and for the price I would recommend that 

 

The link looks to be about 1.25 inch eyepieces, not 2 inch eyepieces . . .

 

Ed

[cbowlsby]

Whether you go with 2” or 1.25” diagonal and visual back, I would consider going with something that has wider AFOV than a Plossl.

Agenda Starguider or the UFF series come to mind and are not that much more expensive than a good Plossl.

[jrmacl]

Hi Again,

 

 

The link looks to be about 1.25 inch eyepieces, not 2 inch eyepieces . . .

 

Ed

yeah I know, but cookjaiii was recommending vixen and TV so I thought I'd just show him where he can pick up the vixen a little cheaper, there aren't many quality brand 2" Plossl to choose from that I know of besides maybe the 55mm TV

 

and I agree with cbowisby, for 2" maybe the 30mm UFF or the 28mm UWA is a better choice especially at f11 

Edited by jrmacl, 20 April 2025 - 02:37 PM.

[TayM57]

One approach is to replace the visual back with a 2" and then convert all your EPs to 2" using adapters. That is what I do for my Morpheus, Delites, and Delos. They're all 2" even though they are 1.25" EPs.

[pianodoc]

Thank you all for your kind words and information. I rarely see Celestron mentioned for eyepieces. I will look into the brands mentioned here.
Is it safe to assume that these companies will make good quality filters as well?
Also, is a set of parfocal EPs a good idea? Any disadvantages?

[vtornado]

Also, is a set of parfocal EPs a good idea? Any disadvantages?

 

Yes you don't have to refocus if you swap eyepieces.  The only truely parfocal plossl I have were televue.  Some other lines are close but I found I had to tweak the focuser a bit.  There are also parafocal rings where you can do it yourself.  Some of the nature of parfocal eyepieces has to do with your eye's ability to compensate for the slight differences.  So there are subjective variables as well.

 

Celestron eyepieces are rebrands of other lines.  I think their plossls are GSO. 

 

Just because a "brand" of eyepiece is good I would not extend that to filters.  Do independent research on filters.  Are you referring to color wratten filters or band pass filters?

Edited by vtornado, 20 April 2025 - 06:57 PM.

[Procyon]

Congrats on the great scope, 9.25" SCT's are very good.

Some quick suggestions that may help you get started: 

 

But before this, read the advice given here (and the posts below by Scott and David) if your scope is a non Edge 9.25" SCT: https://www.cloudyni...-celestron-925/

 

With this setup you avoid having to buy a visual back and avoid extending the focal length of your SCT. 

 

If you must have a visual back for some reason read on..

You can add this visual back: https://agenaastro.c...sct-thread.html or this one which may be sturdier for non edge 9.25" SCT's and a good fit with the Astro-Physics diagonal. (Best to call or email for this one to be sure). 

If your 9.25" SCT is an Edge HD type, it will fit the even sturdier type of visual back: https://www.bhphotov...lock_clamp.html or https://starizona.co...tron-11-14-scts These are excellent types also: https://davidastro.c...&pr_seq=uniform

I have the Baader clamp type on my CPC 11 for 8 years now, it's secure and built like a tank. I've never removed it. These are great in case you bang into the whole optical train and everything goes flying including expensive eyepieces. 

Now if you are going down the astrophotography route, I have no idea if there are better visual backs for photographers. I don't take pictures. Just visual.

Your 2nd buy should be a nice 2" Diagonal like a 2" Baader Clicklock Mirror Diagonal, 2" Astro-Physics, 2" TeleVue Everbrite, or if on a big budget get a 2" Baader BBHS Silver Mirror Diagonal. One of those 4 is all you'll ever need. If on a budget get any 99% 2" Dialectric Mirror Diagonal but it's probably wise to spend a little here.

You really want to stick with Plossls? It's a tough route to take with an SCT. If you want my advice, get 3-4 sharp wide field eyepieces and be done with it, because eventually you'll want better and bigger field of views. But it's also very understandable if you want to go at your own pace and experiment. You can even get a plossl or 2 and skip the 2" parts. When the bug eventually hits you though...

This 20mm AstroTech XWA eyepiece type will be your bread and butter with it's 2mm exit pupil. It'll be great every night you're out there on a lot of objects. Especially on Open Clusters.

After that, it's all up to you and what you want to observe more of. You can get something like a 13mm Astro-Tech XWA if you want to see Galaxies and Globular Clusters more magnified. (A 14/17mm Nikon HW 102 would be even better here). You can also try a Tele Vue 35mm Panoptic, 30mm ES 82, 31mm Tele Vue Nagler or 30mm APM (low magnification widefield types) if you want to observe Nebulae (With a Nebula filter) from a dark site. A 10mm Pentax XW, 10mm TV Delos or 9mm Morpheus would be great for Planets. Those 4 eyepiece types could keep you happy for life even. If you want to spend more money stick around in this forum.

I have an 11" SCT and prefer 90-100º eyepieces over any others, except for planetary viewing (In the 5-12mm range for your scope). If you get Plossls, you can also pair them up in the future for use with a binoviewer on planets.

These websites may help you plan everything out better:

https://www.televue....rn=Advice&id=97

http://www.stargazin...a/scopemath.htm

The viewing difference between a Plossl and a 100º eyepiece:





Good luck, clear skies and have fun.

Edited by Procyon, 21 April 2025 - 04:10 PM.

[pianodoc]

Wow so I’m pretty much a beginner at this point. I thought Plossls were the better design than most but I trust the info I get here more.
As for filters, I just want the best for moon and planets (?ND, red, blue), polarizing? I need to learn more about this before I burden this group with more questions about it.

Thank you!!

[Leafus]

9.25 is great. I’ve had one for years and F10 is forgiving of eyepieces.
First don’t buy under 10mm plossl unless you like polishing glass with your eyeball. Buy a decent Barlow for lower focal length. Celestron omni can be had for little money and are good.
You don’t mention budget but an 8-24 Baader zoom works great with the 9.25 - perfect range for most everything. Add a 32mm plossl, and that worked great for me for a year. When comparing to plossls the narrow FOV of the Baader zoom is equivalent at 24mm and far wider at 8mm.
There are few targets you can’t fit in the 32mm plossl that you can with max SCt FOV in a two inch. SCT don’t go wide. For wide targets you’ll eventually add a refractor.
Eventually you’ll want some two inch but it won’t be plossl but wider AFOV eyepieces at 28mm+.
If budgets tight then Spend a couple of hundred on the Baader and keep the 1.25 for now then go 2inch later.
I’ve got loads of EPs now: ethos, Naglers and others but that Baader is still often in.

[Jay_Reynolds_Freeman]

Plossls are fine. Orthoscopics will do also. I myself prefer Brandons -- which are relatively expensive -- because they scatter noticeably less light, which results in improved contrast.

 

f/10 is indeed forgiving of eyepieces.

 

I suggest that your lowest magnification eyepiece should be one that takes as much advantage as possible of the field of view that a two-inch focus tube provides -- and do get that adapter. What magnification it should be depends on how bright your sky is and on how wide the pupils of your eyes will dilate in darkness. A 40 mm Plossl would work well for many.

 

Your next eyepiece up should be one for deep-sky observing. Preferences vary, but folks seem to end up with an exit pupil between 1.5 mm and 2.5 mm. That would be a focal length of 15 to 25 mm at f/10. Wide fields are nice but not strictly necessary: Most of what you will be looking at will be smaller than the field of view of this eyepiece, and once found with your low-magnification eyepiece will center up nicely.

 

Magnifications for the Moon, planets and double stars generally start with a 1 mm exit pupil. A 10 mm focal length is a good choice for a starter. If you are seriously into these objects, you will want more choices, but what they are will depend on what you want to look at and what seeing is likely.

 

Zoom eyepieces can be very useful. Several makers offer 8-24 mm zoom eyepieces that will work well at f/10. SvBONY has a 3-8 mm zoom that might be a good high-magnification eyepiece, but I myself have not tried one.

 

 

Clear sky ...

[jrmacl]

Thank you all for your kind words and information. I rarely see Celestron mentioned for eyepieces. I will look into the brands mentioned here.
Is it safe to assume that these companies will make good quality filters as well?
Also, is a set of parfocal EPs a good idea? Any disadvantages?

the Celestron X-Cel LX seem to be a decent ep for the price, I've been eyeing the 7mm as maybe a low cost ep since I would only be able to use it in my C8 when the seeing allows.

 

The Astromania (and other rebrands) 22mm 70* ep is said to be very good for the price.

 

If I had a 9.25" I would definitely want a 2" diagonal, and the like Procyon suggested the 20mm XWA, but just keep in mind that like others have said, SCT's are not really "widefield" scopes. With my C8 I really couldn't make up my mind, then I lucked out and got a free f4.5 8" Dob- suddenly I could get the same widefield view and mag with my stock 25mm SMA that I would have got in my C8 with a 55mm Plossl, my cheapy Meade 18mm SWA gives me the same FOV and mag a 41mm Pan would get me in the C8. So yeah, go for 2" on your 9.25" SCT but also maybe think about getting a widefield scope to compliment it. For the price of one or two decent 2" ep's you should be able to get something around a 6" to 8" f4.5 - f6 Dob, and getting a second scope is, as I found out, like doubling up on they eyepieces you already have.

Edited by jrmacl, 20 April 2025 - 11:40 PM.

[eblanken]

Hello (aka Pianodoc),

 

Some have mentioned a ZOOM. I agree that a ZOOM is good to have in your kit. A premium ZOOM is the APM Super-ZOOM which I own and recommend to you. It goes from 15.4mm to 7.7mm while keeping a wider-than-plossl Apparent Field of View of 67 Degrees, which is wider than many ZOOMs.

 

What would match up well with this APM Super-ZOOM is a Pentax XW 40mm 68 Deg. to get widest True Field of View (TFoV) as a "Finder Eyepiece" to start well.

 

Best,

 

Ed

 

P.S. PM me . . . 

Edited by eblanken, 21 April 2025 - 12:25 AM.

[Etien]

Hello, i have a 9.25, for viewing and comfort for me the best setup is: (not cheap)

as said before start with a 

SCT Baader Clicklock 2”

2" Baader Clicklock Mirror Diagonal
Then:
Baader Planetarium Baader Maxbright II Binoviewer

2x Televue panopticon 24”

There is no way back

[SeattleScott]

This has been kind of alluded to but might have gotten lost in the noise. You don't need to upgrade your visual back to use 2" eyepieces. You can just buy a 2" SCT diagonal that will attach directly to the scope. Now some prefer to use the Baader Clicklock, which I also have. It is nice, especially when using heavy 2" eyepieces, but it also costs most of what an SCT diagonal costs, and you would still need to buy a 2" refractor diagonal to go with it. And you are increasing the magnification around 10% compared to using a 2" SCT diagonal. So the Baader SCT Clicklock is nice for easily changing the viewing angle, but it adds unnecessary cost and reduces the field of view slightly compared to just buying a 2" SCT diagonal. 

 

Plossls are generally sharp eyepieces, but narrow viewing angle compared to more modern options, and they have tight eye relief below 10-15mm focal length. Wider AFOV eyepieces allow fitting a target in view at higher magnification. For small targets like globular clusters, or most galaxies, you don't need the wide AFOV. However, there is a tendency to get spoiled by wide afov. Imagine you have a view home and a view of Mount Rainier, or favorite mountain of your choice. With a small window, you could still see all of Mount Rainier. But don't you really want those floor-to-ceiling windows in order to see not just the mountain, but everything around it? The view of the mountain itself doesn't change, but the view feels more luxurious. Same thing with wide AFOV. Even when looking at small targets, some people appreciate the view feeling luxuriously wide, rather than small and cramped.

[Spikey131]

A weakness of the SCT design is the long focal length and, hence, a narrow native field of view.

 

As such, most users want to maximize the FOV.  This is the main reason for adding a 2” visual back, 2” diagonal and a long focal length 2” eyepiece like a 55mm Plossl.  This is a good idea.

 

The other reason to use a 2” visual back and diagonal is the more robust physical strength of this hardware, very helpful for using heavy eyepieces or binoviewers.

 

The other option to maximize the FOV of your C9.25 is to add a focal reducer.  This device effectively shortens the focal length, and allows you to view the maximum possible aFOV with 1.25” eyepieces like a 32mm Plossl.  It won’t work with 2” eyepieces due to vignetting, but will accomplish the same thing as a 2” setup.  You just need to pick one option.

[davidgmd]

Scott’s right on the money. You can get a Baader 2” diagonal and attach it directly to the SCT by removing the diagonal nosepiece, exposing a female SCT thread on the diagonal body. No need to spend money on both a 2” visual back and a 2” diagonal.
 
If you go that route, you should also get a Baader SCT Lock Ring (2458270, $64), which will allow you to adjust the orientation of the diagonal once it has snugged up to the back of the SCT. Agena has an article that explains it.

  

There are 3 advantages to spending an additional $38 on a Baader 2” SCT ClickLock Visual Back (2956220, $102) and using it instead of the SCT Lock Ring:

1) You can use any 2” diagonal without having to remove the nosepiece.

2) You can easily remove the diagonal, making the scope shorter for storage.

3) You can easily adjust the orientation of the diagonal during an observing session to facilitate eyepiece access.

 
The downside to replacing the visual back, in addition to the additional $38, is that it adds 5.8 oz (164 gm) of weight to the back of the scope and 37 mm to the optical path length. The weight is easily balanced and the wide range of the SCT focuser make the additional path length a non-issue for bringing an eyepiece to focus in my experience. However, it does increase the focal length and f/ratio of the scope a bit. Not enough to degrade the views, also in my experience with an 8” EdgeHD. Magnification will be a bit greater and TFOV will be a bit smaller. Not much. An additional 37 mm is a small % increase over the 2350 mm native focal length of a C9.25.

Edited by davidgmd, 21 April 2025 - 03:05 PM.

[Procyon]

You are both correct, when I was in the process of connecting my Baader Clicklock to an 8" SCT I had, I remember changing my mind about the whole thing because of clearance issues. I sold it all and jumped to an 11" SCT. I corrected my post after bumping into this thread earlier. https://www.cloudyni...-celestron-925/

 

The bigger SCT's (And 9.25 Edges) don't have this issue so I avoided researching all this back than.

Edited by Procyon, 21 April 2025 - 04:04 PM.

[Starman1]

Thank you all for your kind words and information. I rarely see Celestron mentioned for eyepieces. I will look into the brands mentioned here.
Is it safe to assume that these companies will make good quality filters as well?
Also, is a set of parfocal EPs a good idea? Any disadvantages?

Celestron doesn't make eyepieces, they are a reseller like most companies.  They charge more than other companies, often, for the same eyepieces.

Filter companies and eyepiece companies are different.

Good quality nebula filters come from Astronomik, Tele Vue, DGM, Lumicon, ICS, Thousand Oaks, and a few others.

I attach a tutorial about nebula filters.

Parfocal eyepieces is a convenience, but far from necessary.  It's why you have a focuser.

 

As for converting the rear visual back to 2", I recommend it as this will increase your choices in eyepieces and, later, make it easier to mount a heavy camera.

The maximum true field in your scope with 1.25" eyepieces is 0.66°.  With 2" eyepieces, it is 1.12°.  That is a huge difference in field size.

So figure a 2" visual back and 2" diagonal will be expenses you will have.

 

As for eyepieces, the rule is "cheap...well corrected...wide field.  Pick any 2."

A 40mm 2" maximum field eyepiece will be an expensive eyepiece.  A 55-56mm Plössl would have the same true field, but a narrower apparent field.

A possible set of focal lengths for the 2350mm focal length: 40mm, 23-24mm, 15-16mm, 11-12mm, 9-10mm.

I will attach a tutorial about eyepieces.

Attached Thumbnails

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Attached Files

•  EYEPIECE QUALITIES AND ABERRATIONSv.2.docx   21.07KB   10 downloads
•  Choosing a Nebula Filter.docx   14.4KB   5 downloads

[davidgmd]

Don’s point about almost doubling the true field by going to a 2” visual back, diagonal, and eyepieces is really key. I’m repeating it so it doesn’t get lost in all the details.